Same thing happened to me shortly after I bought my car.....there is a small rubber washer/o ring at the bottom of the pump mechanism. It seals when you screw the pump back down. It took me a little while to figure it out, but I noticed it after I took the pump out for inspection. The o ring was in place but very brittle and broken - hence no seal. I went to a local farm supply store (I assume a good hardware store will work) and found a selection of o rings. I bought one just big enough to muscle back on the unit but small enough to be tight. Worked like a champ. I ordered a new style right away since the old style units leak when you pump them and make a mess. I figured as often as we replace filters/hoses I would use the pump enough to justify the $20. The o ring held for several days until my new style arrived - probably would last for a while yet. Hopefully your problem is this simple. Good luck
The swap out went great and I have used the new style since - very nice
